Membrane Potting Methods

ABSTRACT

Apparatus and methods are disclosed which reduce stress formation in potting heads for porous hollow filtration membranes. In one example, there is disclosed a potting sleeve for forming a potting head which includes a first fixed portion and a second portion which is movable relative to the first fixed portion to reduce a peripheral extent thereof. In another example, a method of mounting a porous hollow membrane in a membrane filtration apparatus includes positioning a portion of porous hollow membranes within a mold and introducing a curable potting material into the mold so as to immerse the portion of the porous hollow membranes and at least part of one or more deformable members in the potting material. The method further includes at least partially curing the potting material to form a potting head and removing the potting head and the one or more deformable members from the mold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of and claims benefit under 35 U.S.C. § 120 to co-pending U.S. patent application Ser. No. 14/033,968, titled MEMBRANE POTTING METHODS, filed on Sep. 23, 2013, which claims foreign priority benefits under 35 U.S.C. § 119(a)-(d) or 35 U.S.C. § 365(b) from Australian application no. 2012904203, filed Sep. 26, 2012, each of which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND 1. Technical Field

Aspects and embodiments disclosed herein relate generally to methods and apparatus for mounting porous hollow filtration membranes in a membrane filtration system.

2. Discussion of Related Art

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

Synthetic polymeric membranes are well known in the field of ultrafiltration and microfiltration for a variety of implementations, including desalination, gas separation, filtration, and dialysis. The properties of the membranes vary depending on the morphology of the membranes, for example, depending on parameters such as symmetry, pore shape, and pore size, and the chemical nature of the polymeric material used to form the membrane.

A large membrane surface area may be provided when a large filtrate flow is desired. In commercial embodiments, a large number of hollow porous membranes may be mounted together and housed in filtration modules. A commonly used technique to reduce the size of the filtration apparatus is to form the hollow porous membranes in the shape of hollow porous fibers. The hollow porous membranes act in parallel to filter a feed liquid, for example, water for purification. By producing a pressure differential across the membrane walls, the liquid is forced to flow through the pores of the walls of each of the hollow porous membranes while contaminants remain trapped on one side of the membranes and filtrate is withdrawn from the other side. In systems where feed liquid is applied to the outer walls of the membranes (outside-in filtration), the filtrate collects inside the hollow regions, cavities or channels (known as lumens) within the porous hollow membranes and is drawn off through ends of the lumens.

By sealing the ends of a porous hollow membrane in a module pot an impenetrable barrier may be formed between the feed and the filtrate. It is desirable that the seal formed by the barrier between the feed and filtrate be maintained to avoid contamination of the filtrate with feed. It is thus desirable that such module pots be designed to withstand forces such as hydraulic pressure from fluid flow inside the filtration module which might otherwise compromise the seal between the feed and the filtrate.

In addition to sealing the ends of porous hollow membranes, a module pot may be designed to perform further functions including structurally supporting and mounting the membranes within a module or otherwise within a filtration system. In some filtration arrangements, filtrate is withdrawn only from one end of the membranes and the other ends are merely sealed and supported by a potting head. In other arrangements, only one potting head is provided with the membranes being looped with both open ends located in the same potting head.

In some potting arrangements, the porous membrane ends may be sealingly potted using a curable resin material with the porous membrane ends being positioned within the resin material in its liquid non-cured state. The resin material may be allowed to cure to form a generally solid potting head. The curable resin material may be surrounded by a potting sleeve. The potting sleeve may be used to provide an interface between the potting head formed by the cured resin material and associated equipment such as headers and mounting apparatus.

SUMMARY

It has been found that some curable potting materials which may be used to secure filtration membranes within a potting head disposed in a potting sleeve may shrink during the curing process. This shrinkage may result in the formation of residual tensile stress within the potting head due to resistance of the potting sleeve to such shrinkage. Residual tensile stress in potting materials has been found to not only decrease fracture strength and toughness but also to reduce the fatigue life of the materials. The residual tensile stress may cause cracking, splitting, and/or breaking of the potting head. This can result in compromising the separation between the feed liquid and the filtrate stream in a filtration system and possible undesirable contamination of filtrate.

It would be desirable to provide an arrangement of a potting head and potting sleeve in which the formation of residual stress within the potting head during curing of the potting material is reduced as compared to prior known methods.

According to one aspect, there is provided a potting sleeve for use in forming a potting head having a porous hollow membrane mounted therein. The potting sleeve includes a first fixed portion and a second portion which is movable relative to the first fixed portion to reduce a peripheral extent of the second portion.

In some embodiments, the second portion of the potting sleeve is inwardly deformable to reduce the peripheral extent thereof. The second portion of the potting sleeve may include structurally weakened regions configured to provide for the second portion of the potting sleeve to be inwardly deformable. The second portion of the potting sleeve may be formed of a flexible material.

In some embodiments, the potting sleeve includes one or more openings in a wall of the potting sleeve. The openings may be slots.

In accordance with another aspect, there is provided a method of mounting a porous hollow membrane in a potting head of a membrane filtration apparatus. The method comprises providing a mold for receiving potting material and positioning a potting sleeve within the mold. The potting sleeve includes a first fixed portion and a second portion which is movable relative to the first fixed portion to reduce a peripheral extent of the second portion. The method further comprises positioning a portion of the porous hollow membrane to be mounted in a region of the mold encompassed by the potting sleeve, introducing a curable potting material into the region to immerse the portion of the porous hollow membrane in the potting material, at least partially curing the potting material to form the potting head, and removing the potting head and the potting sleeve from the mold.

In some embodiments, the second portion of the potting sleeve is inwardly deformable to reduce the peripheral extent thereof. The second portion of the potting sleeve may include structurally weakened regions configured to provide for the second portion of the potting sleeve to be inwardly deformable. The second portion of the potting sleeve may be formed of a flexible material.

In some embodiments, the potting sleeve is provided with one or more openings in a wall of the potting sleeve. The openings may be slots.

In accordance with another aspect, there is provided a method of mounting a porous hollow membrane in a support structure of a membrane filtration apparatus. The method comprises providing a mold for receiving potting material, positioning one or more deformable members within the mold, positioning a portion of the porous hollow membrane to be mounted within the mold, introducing a curable potting material into the mold to immerse the portion of the porous hollow membrane and at least part of the one or more deformable members in the potting material, at least partially curing the potting material to form the potting head, and removing the potting head and the one or more deformable members from the mold.

In some embodiments, the deformable member comprises a cylindrical plug.

The plug may be hollow and collapsible. The plug may be expandable.

In some embodiments, the deformable member is formed of a flexible material. The deformable member may be formed of a material selected from the group consisting of a soft resin material and rubber.

In some embodiments, an outer surface of the deformable member is provided with engagement formations. The engagement formations may comprise one or more of a groove, a rib, a shoulder, and a fin. The engagement formations may extend axially from a central body of the deformable member. The engagement formations may extend circumferentially from a central body of the deformable member.

In accordance with another aspect, there is provided a structural element for supporting a potting head having a porous hollow membrane mounted therein and extending from a first surface of the potting head. The structural element comprises a cap configured to engage with a potting sleeve of the potting head, the cap having a bearing surface which supports a second surface of the potting head opposite to the first surface of the potting head when the cap is engaged with the potting sleeve.

In some embodiments, the cap is generally cylindrical and the bearing surface includes one or more radially extending ribs. The structural element may extend into the second surface of the potting head. In accordance with another aspect, there is provided a potting sleeve for use in forming a potting head having a porous hollow membrane mounted therein. The potting sleeve includes at least one reinforcement member positioned between inner walls of the potting sleeve, the reinforcement member having opposed sides extending axially of the potting sleeve between a first end portion and an opposed second end portion of the reinforcement member. The reinforcement member is connected to an internal wall of the potting sleeve at connection points on each of the opposed sides of the first end portion and the reinforcement member is free of engagement with the potting sleeve apart from at the connection points.

In some embodiments, the reinforcement member is plate-like. The reinforcement member may be located along a diameter of the potting sleeve.

In some embodiments, the first end portion of the reinforcement member is spaced axially from one end of the potting sleeve.

In some embodiments, the reinforcement member apart from adjacent the connection points is, in use, positioned within the potting head.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 is an elevational view of a top potting sleeve for a membrane sub-module;

FIG. 2 is a plan view of the potting sleeve of FIG. 1;

FIG. 3A is an elevational section view of the potting sleeve of FIG. 1 taken along section B-B of FIG. 2;

FIG. 3B is a similar side elevational sectional view as FIG. 3A with the potting sleeve positioned in a potting mold;

FIG. 4 is a broken elevational view of a membrane sub-module according to another embodiment;

FIG. 5 is an underside perspective view of the lower potting sleeve of the sub-module of FIG. 4;

FIG. 6 is an elevational view of the lower potting sleeve of the sub-module of FIG. 4;

FIG. 7 is an elevational view of a deformable member according to another embodiment;

FIG. 8 is a cross-sectional elevational view of the deformable member of FIG. 7;

FIG. 9 is a top perspective view of a deformable member according to another embodiment;

FIG. 10A is a cross-sectional elevational view of a potting mold with the deformable member of FIG. 7 positioned in use in the potting material together with filtration membranes;

FIG. 10B is a similar view as FIG. 10A of the deformable member of FIG. 7 positioned in use in a potting head;

FIG. 11 is a top perspective view of a potting sleeve with structural extension according to another embodiment;

FIG. 12 is a top perspective cross sectional view taken along a diameter of the potting sleeve of FIG. 11;

FIG. 13 is an exploded top perspective view of an upper portion of a membrane sub-module employing the potting sleeve according to the embodiment of FIGS. 11 and 12;

FIG. 14 is a top perspective cross sectional view taken along a diameter of the membrane sub-module of FIG. 13 in assembled form;

FIG. 15 is a cross sectional elevational view of the sub-module of FIG. 14;

FIG. 16 is an elevational view of an upper potting sleeve according to another embodiment;

FIG. 17 is a top perspective cross sectional view taken along a diameter of the potting sleeve of FIG. 16 with potting resin in the potting sleeve; and

FIG. 18 is a top perspective cross sectional view taken along a diameter of the potting sleeve of FIG. 16 without potting resin in the sleeve.

DETAILED DESCRIPTION

Aspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects disclosed herein are capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Aspects and embodiments disclosed herein are directed to filtration modules or sub-modules and to methods of forming same. Aspects and embodiments disclosed herein provide for a reduced amount of residual stress in potting material of the potting heads of the filtration modules or sub-modules after formation of the potting heads as compared to prior known methods and apparatus. This reduction in residual stress may reduce the chances of mechanical failure of the potting head, for example, delamination of membranes from the potting material in which they are retained, delamination of the potting material from a potting sleeve in which it may be disposed, cracking of the potting material, or other forms of mechanical failure. Aspects and embodiments disclosed herein also provide for a membrane module to include a potting head having a potting material layer thickness with a strength greater than prior known potting heads having potting material layers of equivalent thicknesses.

In some embodiments, a potting sleeve for use in forming a filtration membrane module may be provided with one or more features to at least partially alleviate mechanical stresses which may develop within a potting material during curing of the potting material in the potting sleeve. Many potting materials shrink upon curing, resulting in tensile stresses forming in the potting material if the potting material is constrained to maintain set dimensions during curing. In some embodiments disclosed herein a potting sleeve into which a potting material may be introduced and then cured includes one or more features which provide for one or more dimensions of one or more portions of the potting sleeve to decrease during the curing of the potting material. The decrease in the one or more dimensions of the potting sleeve during curing of the potting material accommodates at least some of the shrinkage of the potting material thus reducing the tendency for tensile stresses to develop in the curing potting material.

In other embodiments one or more stress relieving features may be disposed in the curing potting material in a potting sleeve. The one or more features may expand or be displaced during the curing of the potting material, relieving mechanical stresses which might otherwise develop in the curing potting material.

Referring to FIGS. 1 to 3 there is shown one embodiment of an upper or top potting sleeve for a membrane sub-module 4. The potting sleeve 5 is generally cylindrical though it will be appreciated that the cross-sectional shape of the potting sleeve is not critical and many suitable cross-sectional shapes may be used depending on the desired geometric shape of the potting head. For example, in various embodiments, the potting sleeve 5 may have an elliptical, square, rectangular, or triangular cross-section.

The outer surface 6 of the potting sleeve 5 may be provided with a number of engagement formations. The engagement formations may comprise, for example, circumferentially extending grooves, shoulders, or ribs on outer surface 6 of the potting sleeve 5. It will be appreciated by those in the art that, depending on specific implementations, a variety of different forms and shapes of formation may be used to provide for engagement of the potting sleeve 5 and its associated potting head with other components of the membrane sub-module 4.

A lower portion of the potting sleeve 5 is provided with a circumferential, outwardly extending rib 7 which, in use, is supported on a shoulder provided in the housing of the sub-module (not shown). Above the rib 7, two axially spaced rows of circumferentially spaced through-openings 8 and 9 are provided in the wall of the potting sleeve 5. The openings 8, 9 are shown are circular holes but it will be appreciated the shape and size of the openings is not critical and, in embodiments where openings are desired, any suitable form of opening may be used. For example, the openings 8, 9 may be in the form of circular holes, oval holes, slits, slots, or other shapes.

Above the openings 8, 9, a pair of circumferential, outwardly extending ribs 10 and 11 form a groove 12 which, in use, accommodates a sealing O-ring (not shown). A further circumferential, outwardly extending rib 13 is provided above and vertically spaced from the ribs 10 and 11 to define a supporting shoulder 13′. In some embodiments, it may be desirable to provide ribs 10, 11, and 13 in a region of the potting sleeve 5 which is substantially rigid to ensure the integrity of any mounting or sealing arrangements or structures.

An upwardly extending skirt portion 14 is provided above the rib 13. The skirt portion 14 includes a circumferential groove 15 in its base portion 16 and a reduced diameter inset upper portion 17 with a further circumferential groove 18 positioned between the base portion 15 the upper extent of the inset portion 17. This groove 18 serves to form an outwardly extending lip 19 at the upper extent of the inset portion 17. The lip 19 may be used to engage with a lifting mechanism (not shown) to remove the sub-module from the filtration apparatus.

The skirt portion 14 forms a portion of the potting sleeve 5 which it movable relative to the fixed lower portion of the sleeve. The skirt portion 14 may be utilized to reduce the peripheral extent of the movable portion of the potting sleeve 5. The skirt portion 14 may include a plurality of circumferentially spaced, vertically extending slots 20 formed therein to define deformable or flexible finger portions 21 therebetween.

As best shown in FIGS. 3A and 3B, in use, the upper potting sleeve 5 is positioned in a potting mold 23, together with the membranes 24 to be potted, and is filled with potting material 22 from a level just below the upper set of through-openings 9 to above the upper extent of the potting sleeve 5. The potting material 22 may include any material which may retain filtration membranes 24 within the potting sleeve 5. The potting material 22 may include, for example, urethane, resin, epoxy, or other suitable materials. In some embodiments, the membrane pot may be formed from more than a single layer of potting material, for example, as disclosed in co-pending U.S. patent application Ser. No. 13/087,548, which is incorporated herein by reference in its entirety for all purposes. When more than one layer of potting material is used the layers may be formed of different materials. For example a lower layer distal from the side of the potting head from which the membranes 24 emerge may be formed of a material which strongly adheres to the membranes 24 but is relatively rigid, for example, an epoxy material. A softer potting material, for example, a urethane material may form a layer above the rigid layer. The membranes 24 may emerge from the softer potting material. The softer potting material may flex in use providing for the membranes 24 to move slightly at the point they enter the softer potting material, which may decrease the chances for the membranes 24 to shear from the potting head.

In some embodiments, the inner surface of the potting sleeve 5 may include one or more layers of material which may promote adhesion of the potting material 22 to the potting sleeve, and/or which may elastically deform to facilitate the reduction in mechanical stresses in the cured potting material 22. The one or more layers of material may include, for example, a layer of a urethane material.

As the potting material 22 cures and contracts, the wall of the portion of the potting sleeve 5 defined by the flexible finger portions 21 may deform radially inward to reduce the peripheral extent of skirt portion 14 of the potting sleeve 5 and reduce or eliminate mechanical stresses which might otherwise form within the cured potting material.

It will be appreciated that although slots 20 may be utilized in some embodiments to weaken the skirt portion 14 and provide a movable portion of the potting sleeve 5 to reduce the peripheral extent thereof by inward deformation of the sleeve wall, a variety of other configurations may be used to achieve a similar result in providing for deformability of the potting sleeve. The slots 20 may be replaced by or augmented with thin flexible regions which enable the finger portions 21 to flex inwardly. Further, in some embodiments, the potting sleeve 5 or a portion of the potting sleeve may be formed from a deformable or flexible material. The flexible material may be any material which may adhere to potting material 22 which may be used to retain filtration membranes within the potting sleeve 5 and which has sufficient flexibility to contract along with the potting material 22 upon curing. The flexible material may include, for example, urethane or rubber. In some embodiments, the flexible material may be urethane including a flexibilizing agent.

In another embodiment, the wall of the potting sleeve or a portion thereof may be formed of a number of radial segments which move circumferentially relative to one another to produce an inwardly collapsible configuration. Further, although the slots 20 are shown as extending generally vertically, it will be appreciated that they may extend at an angle to vertical, if desired. For example, the slots may extend horizontally, breaking the skirt 14 into a plurality of horizontal finger-like segments or may form a spiral in the skirt 14.

Referring to FIGS. 4 to 6, there is shown an embodiment of a lower potting sleeve 30. The lower potting sleeve 30 is generally similar in configuration to the upper potting sleeve 5 described above and may include any one or more of the features of the upper potting sleeve 5.

FIG. 4 shows a broken perspective view of a membrane sub-module 4 with an upper potting sleeve 5 and a lower potting sleeve 30.

As shown in FIGS. 5 and 6, the lower potting sleeve 30 has a smooth-walled fixed upper portion 31 divided from a fixed middle portion 32 by a circumferential outwardly extending or protruding locating shoulder 33. In a similar manner to the upper potting sleeve 5, the middle portion 32 of the lower potting sleeve wall 34 is provided with a series of vertically spaced rows of through-openings 35. The through-openings 35 in each row are circumferentially spaced from one another and formed in circumferentially spaced groups 36 consisting of a number of rows of through-openings 35. The through-openings 35 are illustrated as are rounded slots, however, it will be appreciated the form, shape, size, and number of the through-openings 35 is not critical and any suitable form or number of through-openings 35 may be employed. In use, these openings 35 provide for fluid communication with the membranes mounted in the potting head.

The lower extent of the middle portion 32 of the sleeve 30 is defined by a further circumferential, outwardly extending locating shoulder 37. Adjacent and above the locating shoulder 37, a further row of circumferentially spaced slot openings 38 are provided in the sleeve wall. It will be appreciated the form, shape, size, and number of the openings 38 is not critical and any suitable form or number of openings 38 may be employed.

A lower skirt 39 extends downwardly below the shoulder 37 and has a circumferential groove 40 formed therein. In a similar manner to the skirt 14 of the upper potting sleeve 5, the lower skirt 39 is movable relative to the fixed upper portion 31 and the fixed middle portion 32 of the lower porting sleeve 30. The lower skirt 39 includes a plurality of circumferentially spaced, vertically extending slots 41 formed therein to define deformable or flexible finger portions 42 therebetween. The lower skirt 39 thus forms a movable portion of the potting sleeve to reduce the peripheral extent thereof by deformation of the flexible finger portions 42. As potting material disposed within the potting sleeve 30 cures and contracts, the wall 34 of the lower potting sleeve 30 defined by the flexible finger portions 42 can move radially inward to reduce the peripheral extent of skirt 39 of the potting sleeve 30 to reduce or eliminated stresses which might otherwise be formed within the cured potting head.

Although the embodiments described above include openings in the potting sleeves and a variety of engagement formations formed in the outer surfaces of the potting sleeves, it will be appreciated these features are not critical and embodiments comprising a simple plain potting sleeve without openings or particular engagement formations could be employed provided the potting sleeve includes a movable portion which enables the peripheral extent of the potting sleeve to be reduced when the potting material shrinks during curing, thus reducing the potential for mechanical stresses to develop within the potting material.

Referring to FIGS. 7 to 10B, another embodiment of a potting head 52 is illustrated. In this embodiment a deformable member 50 is positioned in the potting material 51 during the potting process so as to relieve stresses produced during the curing of the potting material 51.

As will be appreciated, a variety of different forms of deformable member 50 may be used to achieve the desired function. Embodiments disclosed herein are not limited to the type of deformable member 50 illustrated in FIGS. 7 to 10B. Further, although a single deformable member 50 is shown in FIGS. 10A and 10B, it will be appreciated that a number of deformable members 50 may be positioned as desired throughout the potting head 52.

One embodiment of a suitable deformable member 50 is shown in FIGS. 7 and 8. The deformable member 50 comprises a generally cylindrical, hollow, elongate plug 55. One end of the plug 55 is formed with a conical head 56 while the other end is formed with an enlarged diameter base portion 57. The outer wall of the elongate plug 55 is provided with outwardly extending engagement formations for providing engagement with the potting material of the potting head. The engagement formations may comprise longitudinally extending fins 58 spaced at 90° intervals around the circumference of the plug 55. It will be appreciated that more or fewer than four longitudinally extending fins 58 may be utilized and that these fins 58 need not be spaced at 90° intervals but may be spaced at any particular angular interval or intervals desired. Further, in some embodiments, the fins 58 need not extend along the lateral extent of the deformable member 50 as illustrated, but may alternatively or additionally be in the form of rings or tabs extending from a central body of the deformable member with surfaces arranged normal to the lateral extent of the central body of the deformable member 50 or at other angles as desired. It will be appreciated that any suitable form of engagement formation may be used, for example, grooves, ribs, shoulders, dimples, or formations of other shapes.

The embodiment shown in FIG. 9 illustrates another form of the engagement formations. In this embodiment the outer wall or surface of the plug is provided with a series of axially spaced circumferential grooves 59. It will be appreciated that in other embodiments, the deformable member 55 may assume even additional shapes. For example, the central body of the deformable member need not by cylindrical as illustrated, but may rather be formed with a square, rectangular, oval, or polygonal cross section, or any other cross section as desired. Further, the cross-sectional area of the central body of the deformable member 55 may vary along its lateral extent, for example, expanding or decreasing from a base to a tip of the deformable member 55.

The plug 55 may be hollow and may be made of thin molded plastic material. In use, the thin plastic material may deform due the heat released by the exothermic reaction which occurs during curing of the potting material 52. In other embodiments, the deformable plug may be formed of pre-molded rubber which can readily adhere to the potting material.

In another embodiment, the deformable plug 55 can be molded from a soft resin material, for example, urethane a short time (for example, about 30 minutes) before pre-potting of the membranes. The soft urethane plug can then be located in the potting material to ensure chemical bonding between the plug and the potting material of the potting head. The soft resin material provides a readily deformable plug.

The deformable plug 55 may be molded in a mold coated with polytetrafluoroethylene or another non-stick material to ensure the outer surface of the plug is free of mold release agent which could hinder the chemical bond between the plug 55 and the potting material of the potting head.

FIGS. 10A and 10B show one embodiment of the deformable plug 55 located within a potting head 52.

In use, the plug 55 is attached by means of the enlarged base portion 57 to a pre-potting dish 59′. The plug 55 is then located within the potting mold 23 together with the membranes 24 to be potted, the potting sleeve 5 and potting material 51 introduced into the potting mold 23. The conical head 56 of the plug 55 assists deflection of the membranes 24 away from the plug 55 during the insertion of the membranes into the potting mold 23. The mold 23 may be centrifuged to facilitate correct distribution of the potting material 51 around the membranes 24. Following curing of the potting material 51, the base 57 of the plug may be sliced off leaving the plug 55 flush with the top of the potting head 52.

The soft core or cores created within the potting head 52 by the deformable plug 55 will stretch or otherwise deform allowing the potting material 51 to shrink as it cures, avoiding much of the residual stress which might otherwise be produced by the shrinkage. The reduction in residual stresses within the potting head 52 may lead to a reduction in stress at the membrane-potting material interface.

FIGS. 11 to 14 show a further embodiment of a potting head arrangement including a mechanism for mechanically reinforcing the potting head. In some prior methods as the size of a potting head increases, the thickness of the potting head is increased to resist fluctuating pressures within the membrane sub-module during use. The increased thickness of the potting head results in excessive usage of potting material and the consequent increase in weight of the sub-module. Further, the increased thickness of the potting head may result in an undesirable lumen pressure drop in the length of the membrane as the length of the membrane operating at maximum flow may be substantially increased. Accordingly, where possible, it is desirable to minimize the thickness of the potting head while maintaining its mechanical strength.

It has been recognized that increasing the size of a potting head may increase the desirability of providing a structure to reinforce the potting head to reduce deflection of the potting material and prevent breakage and cracking of the potting material or potting head during use. Incorporating reinforcing elements such as ribs within the potting head, however, may result in a pot structure which is rigid and stiff and which may resist the shrinkage of potting material during curing, thus providing for the formation of residual mechanical stresses in the cured potting material. It has been found that where there is no connection between the reinforcing elements and the potting sleeve surrounding the potting material, a large shear stress may be produced between the internal walls of the potting sleeve and the potting material during curing. Alternatively, where no reinforcing elements are provided, deflection of the potting head and/or potting material during use when exposed to high pressures in a filtration system may be undesirably large. It has been found desirable to provide reinforcement of the potting material without producing excessive stress between the potting material and the potting sleeve during curing. Further, by providing a supporting structural element, the mechanical integrity of the potting head can be maintained while providing a potting material layer which is more resistant to deformation than a potting material layer of an equivalent thickness which is not reinforced with a supporting structural element.

FIGS. 11 and 12 show perspective views of an extension fitting 60 for a potting sleeve 61. The extension fitting 60 includes structural element 62 for supporting a potting head 63 having one or more porous hollow membranes (not shown) mounted therein and extending from a first surface thereof. The structural element 62 comprises a cap 64 configured to engage with a potting sleeve 61 of the potting head 63. The cap 64 has a bearing surface 65 which supports a second surface 66 of the potting head 63 opposite the first surface of the potting head 63 which forms an interface with the porous hollow membranes disposed in the potting head 63 when the cap 64 is engaged with the potting sleeve 61. The bearing surface 65 may comprise the lower surfaces of a series of radially extending ribs 67 which are equally spaced around the circumference of an inner wall of the generally cylindrical cap 64. The ribs 67 extend diametrically of the cylindrical cap 64. The cylindrical cap 64 has a downwardly extending skirt portion 68 below the lower surface 65 of each rib 67 and engages with a reduced diameter stepped portion 69 of the potting sleeve 61. It will be appreciated that other forms of ribs 67 may additionally or alternatively be included in the cap 64. For example, the ribs 67 may include one or more rings which may be disposed concentrically within the cap, and/or may include ribs which are non-equally spaced around the circumference of the inner wall of the cap 64.

FIGS. 13 and 14 show the use of the extension fitting in a membrane module 70. In this embodiment, the potting sleeve 61 and cap 64 slide into a generally cylindrical module housing 71, although it will be appreciated that the module housing 71, potting sleeve 61, and cap 64 may in other embodiments have alternative cross sections, for example, square or rectangular cross sections. The module cap 64 is removably engaged with the top of the module housing 71 and applies an axial support force to the surface 66 of the potting head 63 to prevent deflection thereof under fluctuating pressure from within the sub-module during use.

It will be appreciated that although a bearing surface comprising the lower surfaces of the series of radially extending ribs 67 is shown in FIGS. 11 to 14 a variety of forms of bearing surface could alternatively or additionally be used. For example, a cylinder having a generally flat bearing surface corresponding to the upper surface of the potting head could also or alternatively be used.

FIGS. 16 to 18 show another embodiment of a potting sleeve. The overall configuration of the potting sleeve is similar in configuration to the sleeve shown in FIGS. 5 and 6. Designations are the same for the same features in each embodiment.

The potting sleeve 30 includes at least one reinforcement member 80 positioned between inner walls of the potting sleeve 30. The reinforcement member 80 has opposed sides 82 and 83 extending axially of the potting sleeve 30 between a first end portion 84 and an opposed second end portion 85 of the reinforcement member 80. The reinforcement member is connected to an internal wall of the potting sleeve 30 at connection points 86, 87 on each of the respective opposed sides 82 and 83 of the first end portion 84. The reinforcement member 80 is free of engagement with the potting sleeve 30 apart from at the connection points 86, 87.

As best shown in FIG. 17 the reinforcement member 80 is generally plate-like and the connection points 86 and 87 are outwardly extending portions at the lower ends of each opposed side 82 and 83 of the reinforcement member 80. In use, the upper non-fixed portion of the reinforcement member 80 is embedded in the potting head material 88. The non-fixing of this portion enables the reinforcement member 80 to move during curing and shrinking of the potting material 88 and thus undue stresses between the potting head material 88 and the inner surface of the potting sleeve 30 are reduced or avoided. It will be appreciated that a similar form of potting sleeve could be employed for the upper potting sleeve of the membrane sub-module. The form, shape and dimensions of the reinforcement member 80 are not critical. For example, the reinforcement member 80 may in alternate embodiments include more than one plate-like member which may be parallel or which may intersect the plate-like member illustrated. The reinforcement member 80 may be in a shape other than the generally rectangular shape illustrated, for example a semi-circular shape. In some embodiments, one or more apertures may be defined in the reinforcement member 80. Further, it will be appreciated that one of more reinforcement members having the desired operational attributes could be used. The reinforcement members may interengage or intersect one another provided they have a portion or portions free to move relative to the potting material 88.

Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, it is to be appreciated that any of the features of any of the embodiments disclosed herein may be combined or substituted for features of any other embodiment disclosed herein. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the disclosure. Accordingly, the foregoing description and drawings are by way of example only. 

What is claimed is:
 1. A potting sleeve for use in forming a potting head having a porous hollow membrane mounted therein, the potting sleeve including a first fixed portion and a second portion which is movable relative to the first fixed portion to reduce a peripheral extent of the second portion.
 2. The potting sleeve of claim 1, wherein the second portion of the potting sleeve is inwardly deformable to reduce the peripheral extent thereof.
 3. The potting sleeve of claim 2, wherein the second portion of the potting sleeve includes structurally weakened regions configured to provide for the second portion of the potting sleeve to be inwardly deformable.
 4. The potting sleeve of claim 1, wherein the potting sleeve includes one or more openings in a wall of the potting sleeve.
 5. The potting sleeve of claim 4, wherein the openings are slots.
 6. The potting sleeve of claim 1, wherein the second portion of the potting sleeve is formed of a flexible material.
 7. A method of mounting a porous hollow membrane in a potting head of a membrane filtration apparatus, the method comprising: providing a mold for receiving potting material; positioning a potting sleeve within the mold, the potting sleeve including a first fixed portion and a second portion which is movable relative to the first fixed portion to reduce a peripheral extent of the second portion; positioning a portion of the porous hollow membrane to be mounted in a region of the mold encompassed by the potting sleeve; introducing a curable potting material into the region to immerse the portion of the porous hollow membrane in the potting material; at least partially curing the potting material to form the potting head; and removing the potting head and the potting sleeve from the mold.
 8. The method of claim 7, wherein the second portion of the potting sleeve is inwardly deformable to reduce the peripheral extent thereof.
 9. The method of claim 8, wherein the second portion of the potting sleeve includes structurally weakened regions configured to provide for the second portion of the potting sleeve to be inwardly deformable.
 10. The method of claim 7, wherein the potting sleeve is provided with one or more openings in a wall of the potting sleeve.
 11. The method of claim 10, wherein the openings are slots.
 12. The method of claim 7, wherein the second portion of the potting sleeve is formed of a flexible material.
 13. A method of mounting a porous hollow membrane in a support structure of a membrane filtration apparatus, the method comprising: providing a mold for receiving potting material; positioning one or more deformable members within the mold; positioning a portion of the porous hollow membrane to be mounted within the mold; introducing a curable potting material into the mold to immerse the portion of the porous hollow membrane and at least part of the one or more deformable members in the potting material; at least partially curing the potting material to form the potting head; and removing the potting head and the one or more deformable members from the mold.
 14. The method of claim 13, wherein the deformable member comprises a cylindrical plug.
 15. The method of claim 14, wherein the plug is hollow and collapsible.
 16. The method of claim 13, wherein the deformable member is formed of a flexible material.
 17. The method of claim 13, wherein the deformable member is formed of a material selected from the group consisting of a soft resin material and rubber.
 18. The method of claim 13, wherein an outer surface of the deformable member is provided with engagement formations.
 19. The method of claim 18, wherein the engagement formations comprise one or more of a groove, a rib, a shoulder, and a fin.
 20. The method of claim 18, wherein the engagement formations extend axially from a central body of the deformable member.
 21. The method of claim 18, wherein the engagement formations extend circumferentially from a central body of the deformable member.
 22. A structural element for supporting a potting head having a porous hollow membrane mounted therein and extending from a first surface of the potting head, the structural element comprising a cap configured to engage with a potting sleeve of the potting head, the cap having a bearing surface which supports a second surface of the potting head opposite to the first surface of the potting head when the cap is engaged with the potting sleeve.
 23. The structural element of claim 22, wherein the cap is generally cylindrical and the bearing surface includes one or more radially extending ribs.
 24. The structural element of claim 22, wherein the structural element extends into the second surface of the potting head. 25.-29. (canceled) 